In the electric rotary machine such as a motor, a method of manufacturing the iron core by forming a strip into a spirally laminated structure through a rolling-bending process is well known. In such a manufacturing method, the strip is bent into a spiral configuration by rolling one edge thereof with a mill roll. In other words, the strip is rolled by the mill roll so as to thin toward the outer circumferential edge side.
To increase the accuracy of bending by the rolling-bending process, it is necessary to hold an amount of rolling uniform. Even when the amount of rolling is held uniform, however, the post-process curvature of the strip will not be uniform if the strip has thickness variations. In general, the thickness (t) of the strip has variations of about ±3 to 7%. The post-process curvature of the strip varies even when the mechanical property (hardness, tensile strength, elongation property, or the like) of the strip varies.
In an example disclosed in Japanese Patent Laid-Open No. H 1(1989)-164247, whose applicant is the same as that of the present application, a guide comprising a plurality of rollers arranged in an arcuate configuration is provided close to the outlet of a mill roll. The strip is bent to have a specified curvature with a bending force given the rollers provided close to the outlet of the mill roll, while the inner circumferential edge of the strip is rolled by the mill roll.
In an example disclosed in Japanese Patent Laid-Open No. 2000-224817, a pair of mill rolls and a member for restricting the narrowing down of a strip in a widthwise direction thereof are provided. Further, four notches for mounting bolts are provided at even intervals in the outer circumferential portion of an iron core.
In the example disclosed in Japanese Patent Laid-Open No. H 1(1989)-164247, the accuracy of the post-process curvature of the strip is guaranteed by the plurality of rollers arranged in the arcuate configuration close to the outlet of the mill roll. If the variations in the thickness of the strip are large, however, it is difficult to guarantee the accuracy of the curvature of the strip.
In the example disclosed in Japanese Patent Laid-Open No. 2000-224817, although providing the member for restricting the narrowing down of the strip in a widthwise direction, if the strip has thickness variations, it is extremely difficult to guarantee the accuracy of the post-process curvature of the strip after the mill roll process.